Platelet aggregation inhibitors

ABSTRACT

Peptides useful in inhibiting platelet aggregation are disclosed. These peptides contain the binding sequence Har-G-D and are disulfide-bridged cyclic compounds.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. Ser. No. 07/806,558, filed Dec. 13, 1991, now abandoned, which is a continuation-in-part of Ser. No. 07/586,610, filed Sep. 24, 1990, now abandoned, which is a continuation-in-part of Ser. No. 07/542,488, filed Jun. 22, 1990, now abandoned, which is a continuation-in-part of Ser. No. 07/483,229, now U.S. Pat. No. 5,318,899, which is a continuation-in-part of Ser. No. 07/418,028, filed Oct. 6, 1989, now abandoned, which is a continuation-in-part of 07/367,509, filed Jun. 16, 1989, now abandoned.

TECHNICAL FIELD

This invention relates to a group of peptides which are, or are related to, platelet aggregation inhibitors isolated and purified from various snake venoms. These peptides are useful as therapeutic agents for the treatment of, and prevention of, platelet-associated ischemic disorders. More specifically, the invention concerns peptides which block specific receptors for adhesive proteins involved in platelet adherence and aggregation.

BACKGROUND ART

Heart disease is the primary cause of death in most western societies. Death from heart disease is often induced by platelet-dependent ischemic syndromes which are initiated by atherosclerosis and arteriosclerosis and include, but are not limited to, acute myocardial infarction, chronic unstable angina, transient ischemic attacks and strokes, peripheral vascular disease, arterial thrombosis, preeclampsia, embolism, restenosis and/or thrombosis following angioplasty, carotid endarterectomy, anastomosis of vascular grafts, and chronic cardiovascular devices (e.g., in-dwelling catheters or shunts "extracorporeal circulating devices"). These syndromes represent a variety of stenotic and occlusive vascular disorders thought to be initiated by platelet activation either on vessel walls or within the lumen by blood-borne mediators but are manifested by platelet aggregates which form thrombi that restrict blood flow.

Platelet aggregation is mediated by GP IIb-IIIa complex on the platelet membrane surface. GP IIb-IIIa exists on the surface of unstimulated platelets in an inactive form. When platelets are activated by adhesion and the physiological agonists, the GP IIb-IIIa also becomes activated such that it becomes a receptor for fibrinogen (Fg), von Willebrand Factor (vWF), and fibronectin (Fn) (see Phillips et al., Blood (1988) 71:831-843); however, it is the binding of fibrinogen and/or von Willebrand factor that is believed to be principally responsible for platelet aggregation and thrombus formation in vivo. Therefore, substances which specifically inhibit the binding of fibrinogen or von Willebrand factor to GP IIb-IIIa inhibit platelet aggregation and could be candidates for inhibiting thrombus formation in vivo.

Several classes of peptides have been disclosed which block the binding of adhesive proteins to activated platelets and inhibit platelet aggregation. A summary of some of this art is published in WO90/15620, published 27 Dec. 1990. This published application also discloses a group of cyclic peptides which inhibit platelet aggregation selectively, and which are characterized by the adhesive sequence K*-G/Sar-D, wherein K* is a substituted or unsubstituted lysyl residue. The present invention provides additional members of this class.

DISCLOSURE OF THE INVENTION

The invention relates to members of a group of platelet aggregation inhibitors which are of the formula: ##STR1## wherein K* is a substituted or unsubstituted lysyl residue of the formula R¹ ₂ N(CH₂)₄ CHNHCO-- as described above,

wherein each R¹ is independently H, alkyl (1-6C), or at most one R¹ is R² --C═NR³,

wherein R² is H, alkyl(1-6C) or is a substituted or unsubstituted phenyl or benzyl residue, or is NR⁴ ₂ in which each R⁴ is independently H or alkyl(1-6C), and

R³ is H, alkyl(1-6C), phenyl or benzyl, or

R² --C═NR³ is a radical selected from the group consisting of: ##STR2## where m is an integer of 2-3, and each R⁵ is independently H or alkyl(1-6C);

and wherein one or two (CH₂) may be replaced by O or S provided said O or S is not adjacent to another heteroatom;

AA₁ is a small, neutral (polar or nonpolar) amino acid and n1 is an integer of 0-3;

AA₂ is a neutral, nonpolar large (aromatic or nonaromatic) or a polar aromatic amino acid and n2 is an integer of 0-3;

AA₃ is a proline residue or a modified proline residue (as defined below) and n3 is an integer of 0-1;

AA₄ is a neutral, small amino acid or the N-alkylated form thereof and n4 is an integer of 0-3;

each of X₁ and X₂ is independently a residue capable of forming a bond between X₁ and X₂ to obtain a cyclic compound as shown; and

each of Y₁ and Y₂ is independently a noninterfering substituent or may be absent;

wherein one or more peptide linkages may optionally be replaced by a linkage selected from the group consisting of --CH₂ NH--, --CH₂ S--, CH₂ CH₂ --, --CH═CH-- (cis and trans), --COCH₂ --, --CH(OH)CH₂ -- and --CH₂ SO--;

with the proviso that if n3 is 0; either:

1) the sum of n2 and n4 must be at least 2; or

2) K* must be other than Har or K; or

3) X₂ must be other than cys (C), penicillamine (Pen), or 2-amino-3,3-cyclopentanemethylene-3-mercaptopropionic acid (APmp); or

4) Y₁ or Y₂ must comprise at least one amino acid residue; or

5) one or more peptide linkages is replaced by said alternate linkage.

This invention concerns, specifically, compounds of the formula:

PAI 80 (SEQ ID NO:1) Mpr-P-Har-G-D-W-P-C-NH₂

PAI 81 (SEQ ID NO:2) Mpr-G-Har-G-D-W-P-C-NH₂

PAI 82 (SEQ ID NO:3) Mpr-A-Har-G-D-W-P-C-NH₂

PAI 83 (SEQ ID NO:4) Mpr-Aib-Har-G-D-W-P-C-NH₂

PAI 84 (SEQ ID NO:5) Mpr-(N-Me-Arg)-Har-G-D-W-P-C-NH₂

PAI 85 (SEQ ID NO:6) Mpr-(N-Me-Ser)-Har-G-D-W-P-C-NH₂

PAI 86 (SEQ ID NO:7) Mpr-D-alanine-Har-G-D-W-P-C-NH₂

PAI 87 (SEQ ID NO:8) Mpr-(β-Ala)-Har-G-D-W-P-C-NH₂

PAI 88 (SEQ ID NO:9) Mpr-(N-Me-Leu)-Har-G-D-W-P-C-NH₂

PAI 89 (SEQ ID NO:10) Mpr-(N-Me-Ala)-Har-G-D-W-P-C-NH₂

PAI 90 (SEQ ID NO:11) Mpr-Sar-Har-G-D-W-P-C-NH₂

PAI 91 (SEQ ID NO:12) Mpr-V-Har-G-D-W-P-C-NH₂

PAI 92 (SEQ ID NO:13) Mpr-S-Har-G-D-W-P-C-NH₂

PAI 93 (SEQ ID NO:14) Mpr-Har-G-D-W-P-A-C-NH₂

PAI 94 (SEQ ID NO:15) Mpr-Har-G-D-W-P-(N-Me-Ala)-C-NH₂

PAI 95 (SEQ ID NO:16) Mpr-Har-G-D-W-P-G-C-NH₂

PAI 96 (SEQ ID NO:17) Mpr-Har-G-D-W-P-A.sup.† -C-NH₂

PAI 97 (SEQ ID NO:18) Mpr-Har-G-D-W-P-P-C-NH₂

PAI 98 (SEQ ID NO:19) Mpr-Har-G-D-W-P-(Sar)-C-NH₂

PAI 99 (SEQ ID NO:20) Mpr-Har-G-D-W-P-(Aib)Cys-NH₂

PAI 100 (SEQ ID NO:21) Mpr-A-(Har)-G-D-W-P-Pen-NH₂

PAI 101 (SEQ ID NO:22) Mpr-A-K-G-D-W-P-Pen-NH₂

PAI 102 (SEQ ID NO:23) Mpr-D-(Har)-G-D-W-P-Pen-NH₂

The invention also concerns pharmaceutical compositions containing the peptides of the invention and methods to inhibit platelet aggregation using these peptides and formulations.

Modes of Carrying Out the Invention

The invention peptides can be synthesized and tested according to the methods described in WO90/15620, published 27 Dec. 1990 and incorporated herein by reference. Furthermore, antibodies may be prepared to these peptides as set forth therein. Briefly, compounds within the scope of the present invention can be synthesized chemically by means well known in the art such as, e.g., solid-phase peptide synthesis. The synthesis is commenced from the carboxy-terminal end of the peptide using an alpha-amino protected amino acid. t-Butyloxycarbonyl (Boc) protective groups can be used for all amino groups even though other protective groups such as fluorenylmethyloxycarbonyl (Fmoc), are suitable. For example, Boc-Gly-OH, Boc-Ala-OH, Boc-His (Tos)-OH, (i.e., selected carboxy-terminal amino acids) can be esterified to chloromethylated polystyrene resin supports, p-methyl benzhydrylamine (pMBHA) or PAM resins. The polystyrene resin support is preferably a copolymer of styrene with about 0.5 to 2% divinyl benzene as a cross-linking agent which causes the polystyrene polymer to be completely insoluble in certain organic solvents. See Stewart, et al., Solid-Phase Peptide Synthesis (1969) W. H. Freeman Co., San Francisco and Merrifield, J Am Chem Soc (1963) 85:2149-2154. These and other methods of peptide synthesis are also exemplified by U.S. Pat. Nos. 3,862,925, 3,842,067, 3,972,859, and 4,105,602.

The synthesis may use manual synthesis techniques or automatically employ, for example, an Applied BioSystems 430A or 431A Peptide Synthesizer (Foster City, Calif.) following the instructions provided in the instruction manual supplied by the manufacturer. Cleavage of the peptides from the resin can be performed using the "low-high" HF deprotection protocols as described in Lu, G.-S., et al., Int J Peptide & Protein Res (1987) 29:545-557. Refolding of analogs of the snake venom PAIs can be performed using the procedure outlined in Garsky, V., et al., Proc Natl Acad Sci USA (1989) 86:4022-4026 which describes the solid-phase synthesis of echistatin.

It will be readily appreciated by those having ordinary skill in the art of peptide synthesis that the intermediates which are constructed in accordance with the present disclosure during the course of synthesizing the present analog compounds are themselves novel and useful compounds and are thus within the scope of the invention.

Alternatively, selected compounds of the present invention can be produced by expression of recombinant DNA constructs prepared in accordance with well-known methods. Such production can be desirable to provide large quantities or alternative embodiments of such compounds. Since the peptide sequences are relatively short, recombinant production is facilitated; however, production by recombinant means is particularly preferred over standard solid phase peptide synthesis for peptides of at least 8 amino acid residues.

Antibodies

Antibodies to the compounds of the invention may be prepared by standard immunization protocols involving administering these compounds to various vertebrates, such as rabbits, rats, mice, sheep, and chickens result in antisera which are immunoreactive with the purified peptide. The compounds of the invention may be advantageously conjugated to a suitable antigenically neutral carrier, such as an appropriate serum albumin or keyhole limpet hemocyanin, in order to enhance immunogenicity. In addition, the free peptide can be injected with methylated BSA as an alternative to conjugation. Furthermore, the antibody-secreting cells of the immunized mammal can be immortalized to generate monoclonal antibody panels which can then be screened for reactivity with the peptides.

The resulting polyclonal or monoclonal antibody preparations are useful in assays for levels of the corresponding peptides in biological samples using standard immunoassay procedures.

Assays

The compounds of the invention are tested for platelet aggregation inhibition (PAI) activity using an assay performed as follows. GP IIb-IIIa, prepared in purified form, for example as described by Fitzgerald, L. A., et al., Anal Biochem (1985) 151:169-177, incorporated herein by reference, is coated onto a solid support such as beads, test tubes, or microtiter plates. The coated support is then contacted with fibrinogen and with the test material and incubated for a sufficient time to permit maximal binding of fibrinogen to the immobilized GP IIb-IIIa. Fibrinogen is typically provided at a concentration of about 5-50 nM and the test material can, if desired, be added at a series of dilutions. Typical incubations are 2-4 hr at 35° C., the time and temperature being interdependent.

After incubation, the solution containing the fibrinogen and test material is removed and the level of binding of fibrinogen measured by quantitating bound fibrinogen to GP IIb-IIIa. Any suitable means of detection may be used, but it is convenient to employ labeled fibrinogen, for example using radioactive, fluorescent or biotinylated labels. Such methods are well known and need not be elaborated here.

Assessment of the results is aided by employing a control sample, usually identical to the test sample except that the test substance is absent. In this case, percent inhibition may be calculated using the amount of Fg bound in the control as representing the basis, so that ##EQU1## Other measures of inhibition effectiveness, such as IC₅₀, may also be used.

The assay systems of the invention further include characterization of the PAI specificity by binding inhibition assays identical to that above but substituting other adhesive proteins for Fg and other receptors for GP IIb-IIIa. In particular, inhibition of the binding of vitronectin to the vitronectin receptor; fibronectin to the fibronectin receptor; fibronectin to GP IIb-IIIa and fibrinogen and/or vWF to GP IIb-IIIa may be assessed. The adhesive protein and receptors for these assays are available in the art.

In addition to the plate assays of the invention, other assays for platelet aggregation inhibition activity and related activities are also available, as set forth above. In summary, a list of commonly employed assays is as follows:

1. The plate assays utilizing specific receptors described in the previous paragraphs;

2. Standard assays directly applied to platelet aggregation, such as those described by Gann, Z.-R., et al., J Biol Chem (1988) 263:19827-19832; Huang, T. F., et al., J Biol Chem (1987) 262:16157-16163; Biochemistry (1989) 28:661-666, cited above and incorporated herein by reference;

3. An in vivo thrombosis model in dogs as described hereinbelow in Example 1, and by Folts, J. D., et al., Circulation (1976) 54:365; and

4. Effect on cell adhesion using S35 methionine-labeled cells as described hereinbelow in Example 19.

Administration and Utility

The PAIs of the invention are useful therapeutically to prevent thrombus formation. Indications appropriate to such treatment include, without limitation, atherosclerosis and arteriosclerosis, acute myocardial infarction, chronic unstable angina, transient ischemic attacks and strokes, peripheral vascular disease, arterial thrombosis, preeclampsia, embolism, restenosis and/or thrombosis following angioplasty, carotid endarterectomy, anastomosis of vascular grafts, and chronic cardiovascular devices (e.g., in-dwelling catheters or shunts "extracorporeal circulating devices"). These syndromes represent a variety of stenotic and occlusive vascular disorders thought to be initiated by platelet activation on vessel walls.

The PAIs may be used for prevention or abortion of arterial thrombus formation, in unstable angina and arterial emboli or thrombosis, as well as treatment or prevention of myocardial infarction (MI) and mural thrombus formation post MI. For brain-related disorders, treatment or prevention of transient ischemic attack and treatment of thrombotic stroke or stroke-in-evolution are included.

The PAIs may also be used for prevention of platelet aggregation, embolization, or consumption in extracorporeal circulations, including improving renal dialysis, cardiopulmonary bypasses, hemoperfusions, and plasmapheresis.

PAIs prevent platelet aggregation, embolization, or consumption associated with intravascular devices, and administration results in improved utility of intraaortic balloon pumps, ventricular assist devices, and arterial catheters.

The PAIs will also be useful in treatment or prevention of venous thrombosis as in deep venous thrombosis, IVC, renal vein or portal vein thrombosis, and pulmonary venous thrombosis.

Various disorders involving platelet consumption, such as thrombotic thrombocytopenic purpura are also treatable.

In addition, the PAIs of the present invention may be used in numerous nontherapeutic applications where inhibiting platelet aggregation is desired. For example, improved platelet and whole blood storage can be obtained by adding sufficient quantities of the peptides, the amount of which will vary depending upon the length of proposed storage time, the conditions of storage, the ultimate use of the stored material, etc.

The PAI dosage can range broadly depending upon the desired affects and the therapeutic setting. Typically, dosages will be between about 0.01 and 10 mg/kg, preferably between about 0.01 to 0.1 mg/kg, body weight. Administration is preferably parenteral, such as intravenous on a daily basis for up to a week or as much as one or two months or more, all of which will vary with the peptide's size. If the peptides are sufficiently small (e.g., less than about 8-10 amino acid residues) other routes of administration can be utilized, such as intranasally, sublingually, or the like.

Injectables can be prepared in conventional forms, either as liquid solutions or suspensions, solid forms suitable for solution or suspension in liquid prior to injection, or as emulsions. Suitable excipients are, for example, water, saline, dextrose, mannitol, lactose, lecithin, albumin, sodium glutamate, cysteine hydrochloride or the like. In addition, if desired, the injectable pharmaceutical compositions may contain minor amounts of nontoxic auxiliary substances, such as wetting agents, pH buffering agents, and the like. If desired, absorption enhancing preparations (e.g., liposomes) may be utilized.

Preparation A Preparation of G-C-G-K-G-D-W-P-C-A-NH₂

One-half mmol of pMBHA resin (0.72 meq/g, Applied Biosystems, Foster City, Calif.) was subjected to Procedure A with the required amino acids (introduced in order). The Boc-protected amino acids had the following side-chain protection: Asp(O-cHex), Cys(4-MeBzl), and Lys(Cl-Z). Following completion of the assembly of the protected peptide-resin, the amino terminal Boc group was removed with TFA and the resin dried as its TFA-salt form. The resin (1.54 g) was treated with anhydrous hydrogen fluoride (HF) containing 10% anisole, 2% ethyl methyl sulfide for 30 min at -10° C., and an additional 30 min at 0° C. The HF was removed in vacuo and the peptide/resin mixture was suspended in diethyl ether followed by alternately washing with chloroform and ether 3X. After a final ether wash, the peptide was extracted from the resin with 2.0M acetic acid, diluted with distilled water and lyophilized.

The crude peptide (370 mg) was dissolved in deoxygenated 10 mM NH₄ OAc, pH 8, to 0.5 mg/ml and allowed to oxidize by dropwise addition of a slight excess of 0.01M potassium ferricyanide (K₃ Fe(CN)₆) solution, stirred an additional 20 min, and adjusted to pH 5 with acetic acid. The peptide solution was treated with DOWEX AG3x4 anion-exchange resin for 15 min with stirring and the resin filtered, diluted with H₂ O and lyophilized to yield the crude cyclized peptide. The crude cyclized peptide (392 mg) was purified by desalting on Sephadex G-25F using 0.5M acetic acid as eluent, followed by ion-exchange chromatography on CM-Sepharose (Pharmacia) using an elution gradient generated by addition of 100 mM NH₄ OAc to a solution of 10 mM NH₄ OAc, pH 4.5. Fractions which had a minimum purity of 90% by HPLC analysis were pooled and lyophilized from H₂ O several time to yield 175 mg. Final purification consisted of preparative HPLC purification on a Water C-18 reverse-phase column with an acetonitrile/water/TFA gradient to yield purified peptide.

EXAMPLE 1 Preparation of Additional Analogs

The following analogs were synthesized in a manner similar to that set forth in Preparation A and were tested for PAI activity in the assay method described hereinabove.

    __________________________________________________________________________                                         Appr. IC.sub.50                            Analog      Sequence                (μM)                                    __________________________________________________________________________     PAI 80 (SEQ ID NO:1)                                                                       Mpr--P--Har--G--D--W--P--C--NH.sub.2                                                                   1.29                                       PAI 81 (SEQ ID NO:2)                                                                       Mpr--G--Har--G--D--W--P--C--NH.sub.2                                                                   7.47                                       PAI 82 (SEQ ID NO:3)                                                                       Mpr--A--Har--G--D--W--P--C--NH.sub.2                                                                   0.12                                       PAI 83 (SEQ ID NO:4)                                                                       Mpr--Aib--Har--G--D--W--P--C--NH.sub.2                                                                 2.20                                       PAI 84 (SEQ ID NO:5)                                                                       Mpr--(N--Me--Arg)--Har--G--D--W--P--C--NH.sub.2                                                        0.25                                       PAI 85 (SEQ ID NO:6)                                                                       Mpr--(N--Me--Ser)--Har--G--D--W--P--C--NH.sub.2                                                        0.28                                       PAI 86 (SEQ ID NO:7)                                                                       Mpr--D-alanine-Har--G--D--W--P--C--NH.sub.2                                                            1.15                                       PAI 87 (SEQ ID NO:8)                                                                       Mpr--(β-Ala)-Har--G--D--W--P--C--NH.sub.2                                                         0.92                                       PAI 88 (SEQ ID NO:9)                                                                       Mpr--(N--Me--Leu)--Har--G--D--W--P--C--NH.sub.2                                                        0.84                                       PAI 89 (SEQ ID NO:10)                                                                      Mpr--(N--Me--Ala)--Har--G--D--W--P--C--NH.sub.2                                                        0.62                                       PAI 90 (SEQ ID NO:11)                                                                      Mpr--Sar--Har--G--D--W--P--C--NH.sub.2                                                                 0.27                                       PAI 91 (SEQ ID NO:12)                                                                      Mpr--V--Har--G--D--W--P--C--NH.sub.2                                                                   0.35                                       PAI 92 (SEQ ID NO:13)                                                                      Mpr--S--Har--G--D--W--P--C--NH.sub.2                                                                   0.24                                       PAI 93 (SEQ ID NO:14)                                                                      Mpr--Har--G--D--W--P--A--C--NH.sub.2                                                                   3.33                                       PAI 94 (SEQ ID NO:15)                                                                      Mpr--Har--G--D--W--P--(N--Me--Ala)--C--NH.sub.2                                                        8.66                                       PAI 95 (SEQ ID NO:16)                                                                      Mpr--Har--G--D--W--P--G--C--NH.sub.2                                                                   8.66                                       PAI 96 (SEQ ID NO:17)                                                                      Mpr--Har--G--D--W--P--A.sup.† --C--NH.sub.2                                                     0.23                                       PAI 97 (SEQ ID NO:18)                                                                      Mpr--Har--G--D--W--P--P--C--NH.sub.2                                                                   1.40                                       PAI 98 (SEQ ID NO:19)                                                                      Mpr--Har--G--D--W--P--(Sar)--C--NH.sub.2                                                               0.31                                       PAI 99 (SEQ ID NO:20)                                                                      Mpr--Har--G--D--W--P--(Aib)Cys--NH.sub.2                                                               0.46                                       PAI 100 (SEQ ID NO:21)                                                                     Mpr--A--(Har)--G--D--W--P--Pen--NH.sub.2                                                               0.37                                       PAI 101 (SEQ ID NO:22)                                                                     Mpr--A--K--G--D--W--P--Pen--NH.sub.2                                                                   4.91                                       PAI 102 (SEQ ID NO:23)                                                                     Mpr--D--(Har)--G--D--W--P--Pen--NH.sub.2                                                               4.04                                       __________________________________________________________________________

    __________________________________________________________________________     SEQUENCE LISTING                                                               (1) GENERAL INFORMATION:                                                       (iii) NUMBER OF SEQUENCES: 23                                                  (2) INFORMATION FOR SEQ ID NO:1:                                               (i) SEQUENCE CHARACTERISTICS:                                                  (A) LENGTH: 8 amino acids                                                      (B) TYPE: amino acid                                                           (C) STRANDEDNESS: single                                                       (D) TOPOLOGY: linear                                                           (ix) FEATURE:                                                                  (A) NAME/KEY: Modified-site                                                    (B) LOCATION: 1                                                                (D) OTHER INFORMATION: /note= "Should be Mpr"                                  (ix) FEATURE:                                                                  (A) NAME/KEY: Modified-site                                                    (B) LOCATION: 3                                                                (D) OTHER INFORMATION: /note= "Should be Har"                                  (xi) SEQUENCE DESCRIPTION: SEQ ID NO:1:                                        XaaProXaaGlyAspTrpProCys                                                       15                                                                             (2) INFORMATION FOR SEQ ID NO:2:                                               (i) SEQUENCE CHARACTERISTICS:                                                  (A) LENGTH: 8 amino acids                                                      (B) TYPE: amino acid                                                           (C) STRANDEDNESS: single                                                       (D) TOPOLOGY: linear                                                           (ix) FEATURE:                                                                  (A) NAME/KEY: Modified-site                                                    (B) LOCATION: 1                                                                (D) OTHER INFORMATION: /note= "Should be Mpr"                                  (ix) FEATURE:                                                                  (A) NAME/KEY: Modified-site                                                    (B) LOCATION: 3                                                                (D) OTHER INFORMATION: /note= "Should be Har"                                  (xi) SEQUENCE DESCRIPTION: SEQ ID NO:2:                                        XaaGlyXaaGlyAspTrpProCys                                                       15                                                                             (2) INFORMATION FOR SEQ ID NO:3:                                               (i) SEQUENCE CHARACTERISTICS:                                                  (A) LENGTH: 8 amino acids                                                      (B) TYPE: amino acid                                                           (C) STRANDEDNESS: single                                                       (D) TOPOLOGY: linear                                                           (ix) FEATURE:                                                                  (A) NAME/KEY: Modified-site                                                    (B) LOCATION: 1                                                                (D) OTHER INFORMATION: /note= "Should be Mpr"                                  (ix) FEATURE:                                                                  (A) NAME/KEY: Modified-site                                                    (B) LOCATION: 3                                                                (D) OTHER INFORMATION: /note= "Should be Har"                                  (xi) SEQUENCE DESCRIPTION: SEQ ID NO:3:                                        XaaAlaXaaGlyAspTrpProCys                                                       15                                                                             (2) INFORMATION FOR SEQ ID NO:4:                                               (i) SEQUENCE CHARACTERISTICS:                                                  (A) LENGTH: 8 amino acids                                                      (B) TYPE: amino acid                                                           (C) STRANDEDNESS: single                                                       (D) TOPOLOGY: linear                                                           (ix) FEATURE:                                                                  (A) NAME/KEY: Modified-site                                                    (B) LOCATION: 1                                                                (D) OTHER INFORMATION: /note= "Should be Mpr"                                  (ix) FEATURE:                                                                  (A) NAME/KEY: Modified-site                                                    (B) LOCATION: 2                                                                (D) OTHER INFORMATION: /note= "Should be Aib"                                  (ix) FEATURE:                                                                  (A) NAME/KEY: Modified-site                                                    (B) LOCATION: 3                                                                (D) OTHER INFORMATION: /note= "Should be Har"                                  (xi) SEQUENCE DESCRIPTION: SEQ ID NO:4:                                        XaaXaaXaaGlyAspTrpProCys                                                       15                                                                             (2) INFORMATION FOR SEQ ID NO:5:                                               (i) SEQUENCE CHARACTERISTICS:                                                  (A) LENGTH: 8 amino acids                                                      (B) TYPE: amino acid                                                           (C) STRANDEDNESS: single                                                       (D) TOPOLOGY: linear                                                           (ix) FEATURE:                                                                  (A) NAME/KEY: Modified-site                                                    (B) LOCATION: 1                                                                (D) OTHER INFORMATION: /note= "Should be Mpr"                                  (ix) FEATURE:                                                                  (A) NAME/KEY: Modified-site                                                    (B) LOCATION: 2                                                                (D) OTHER INFORMATION: /note= "Should be N-Me-Arg"                             (ix) FEATURE:                                                                  (A) NAME/KEY: Modified-site                                                    (B) LOCATION: 3                                                                (D) OTHER INFORMATION: /note= "Should be Har"                                  (xi) SEQUENCE DESCRIPTION: SEQ ID NO:5:                                        XaaXaaXaaGlyAspTrpProCys                                                       15                                                                             (2) INFORMATION FOR SEQ ID NO:6:                                               (i) SEQUENCE CHARACTERISTICS:                                                  (A) LENGTH: 8 amino acids                                                      (B) TYPE: amino acid                                                           (C) STRANDEDNESS: single                                                       (D) TOPOLOGY: linear                                                           (ix) FEATURE:                                                                  (A) NAME/KEY: Modified-site                                                    (B) LOCATION: 1                                                                (D) OTHER INFORMATION: /note= "Should be Mpr"                                  (ix) FEATURE:                                                                  (A) NAME/KEY: Modified-site                                                    (B) LOCATION: 2                                                                (D) OTHER INFORMATION: /note= "Should be N-Me-Ser"                             (ix) FEATURE:                                                                  (A) NAME/KEY: Modified-site                                                    (B) LOCATION: 3                                                                (D) OTHER INFORMATION: /note= "Should be Har"                                  (xi) SEQUENCE DESCRIPTION: SEQ ID NO:6:                                        XaaXaaXaaGlyAspTrpProCys                                                       15                                                                             (2) INFORMATION FOR SEQ ID NO:7:                                               (i) SEQUENCE CHARACTERISTICS:                                                  (A) LENGTH: 8 amino acids                                                      (B) TYPE: amino acid                                                           (C) STRANDEDNESS: single                                                       (D) TOPOLOGY: linear                                                           (ix) FEATURE:                                                                  (A) NAME/KEY: Modified-site                                                    (B) LOCATION: 3                                                                (D) OTHER INFORMATION: /note= "Should be Har"                                  (ix) FEATURE:                                                                  (A) NAME/KEY: Modified-site                                                    (B) LOCATION: 2                                                                (D) OTHER INFORMATION: /note= "Should be D-Ala"                                (ix) FEATURE:                                                                  (A) NAME/KEY: Modified-site                                                    (B) LOCATION: 1                                                                (D) OTHER INFORMATION: /note= "Should be Mpr"                                  (xi) SEQUENCE DESCRIPTION: SEQ ID NO:7:                                        XaaXaaXaaGlyAspTrpProCys                                                       15                                                                             (2) INFORMATION FOR SEQ ID NO:8:                                               (i) SEQUENCE CHARACTERISTICS:                                                  (A) LENGTH: 8 amino acids                                                      (B) TYPE: amino acid                                                           (C) STRANDEDNESS: single                                                       (D) TOPOLOGY: linear                                                           (ix) FEATURE:                                                                  (A) NAME/KEY: Modified-site                                                    (B) LOCATION: 1                                                                (D) OTHER INFORMATION: /note= "Should be Mpr"                                  (ix) FEATURE:                                                                  (A) NAME/KEY: Modified-site                                                    (B) LOCATION: 2                                                                (D) OTHER INFORMATION: /note= "Should be bAla"                                 (ix) FEATURE:                                                                  (A) NAME/KEY: Modified-site                                                    (B) LOCATION: 3                                                                (D) OTHER INFORMATION: /note= "Should be Har"                                  (xi) SEQUENCE DESCRIPTION: SEQ ID NO:8:                                        XaaXaaXaaGlyAspTrpProCys                                                       15                                                                             (2) INFORMATION FOR SEQ ID NO:9:                                               (i) SEQUENCE CHARACTERISTICS:                                                  (A) LENGTH: 8 amino acids                                                      (B) TYPE: amino acid                                                           (C) STRANDEDNESS: single                                                       (D) TOPOLOGY: linear                                                           (ix) FEATURE:                                                                  (A) NAME/KEY: Modified-site                                                    (B) LOCATION: 1                                                                (D) OTHER INFORMATION: /note= "Should be Mpr"                                  (ix) FEATURE:                                                                  (A) NAME/KEY: Modified-site                                                    (B) LOCATION: 2                                                                (D) OTHER INFORMATION: /note= "Should be N-Me-Leu"                             (ix) FEATURE:                                                                  (A) NAME/KEY: Modified-site                                                    (B) LOCATION: 3                                                                (D) OTHER INFORMATION: /note= "Should be Har"                                  (xi) SEQUENCE DESCRIPTION: SEQ ID NO:9:                                        XaaXaaXaaGlyAspTrpProCys                                                       15                                                                             (2) INFORMATION FOR SEQ ID NO:10:                                              (i) SEQUENCE CHARACTERISTICS:                                                  (A) LENGTH: 8 amino acids                                                      (B) TYPE: amino acid                                                           (C) STRANDEDNESS: single                                                       (D) TOPOLOGY: linear                                                           (ix) FEATURE:                                                                  (A) NAME/KEY: Modified-site                                                    (B) LOCATION: 1                                                                (D) OTHER INFORMATION: /note= "Should be Mpr"                                  (ix) FEATURE:                                                                  (A) NAME/KEY: Modified-site                                                    (B) LOCATION: 2                                                                (D) OTHER INFORMATION: /note= "Should be N-Me-Ala"                             (ix) FEATURE:                                                                  (A) NAME/KEY: Modified-site                                                    (B) LOCATION: 3                                                                (D) OTHER INFORMATION: /note= "Should be Har"                                  (xi) SEQUENCE DESCRIPTION: SEQ ID NO:10:                                       XaaXaaXaaGlyAspTrpProCys                                                       15                                                                             (2) INFORMATION FOR SEQ ID NO:11:                                              (i) SEQUENCE CHARACTERISTICS:                                                  (A) LENGTH: 8 amino acids                                                      (B) TYPE: amino acid                                                           (C) STRANDEDNESS: single                                                       (D) TOPOLOGY: linear                                                           (ix) FEATURE:                                                                  (A) NAME/KEY: Modified-site                                                    (B) LOCATION: 1                                                                (D) OTHER INFORMATION: /note= "Should be Mpr"                                  (ix) FEATURE:                                                                  (A) NAME/KEY: Modified-site                                                    (B) LOCATION: 2                                                                (D) OTHER INFORMATION: /note= "Should be Sar"                                  (ix) FEATURE:                                                                  (A) NAME/KEY: Modified-site                                                    (B) LOCATION: 3                                                                (D) OTHER INFORMATION: /note= "Should be Har"                                  (xi) SEQUENCE DESCRIPTION: SEQ ID NO:11:                                       XaaXaaXaaGlyAspTrpProCys                                                       15                                                                             (2) INFORMATION FOR SEQ ID NO:12:                                              (i) SEQUENCE CHARACTERISTICS:                                                  (A) LENGTH: 8 amino acids                                                      (B) TYPE: amino acid                                                           (C) STRANDEDNESS: single                                                       (D) TOPOLOGY: linear                                                           (ix) FEATURE:                                                                  (A) NAME/KEY: Modified-site                                                    (B) LOCATION: 1                                                                (D) OTHER INFORMATION: /note= "Should be Mpr"                                  (ix) FEATURE:                                                                  (A) NAME/KEY: Modified-site                                                    (B) LOCATION: 3                                                                (D) OTHER INFORMATION: /note= "Should be Har"                                  (xi) SEQUENCE DESCRIPTION: SEQ ID NO:12:                                       XaaValXaaGlyAspTrpProCys                                                       15                                                                             (2) INFORMATION FOR SEQ ID NO:13:                                              (i) SEQUENCE CHARACTERISTICS:                                                  (A) LENGTH: 8 amino acids                                                      (B) TYPE: amino acid                                                           (C) STRANDEDNESS: single                                                       (D) TOPOLOGY: linear                                                           (ix) FEATURE:                                                                  (A) NAME/KEY: Modified-site                                                    (B) LOCATION: 1                                                                (D) OTHER INFORMATION: /note= "Should be Mpr"                                  (ix) FEATURE:                                                                  (A) NAME/KEY: Modified-site                                                    (B) LOCATION: 3                                                                (D) OTHER INFORMATION: /note= "Should be Har"                                  (xi) SEQUENCE DESCRIPTION: SEQ ID NO:13:                                       XaaSerXaaGlyAspTrpProCys                                                       15                                                                             (2) INFORMATION FOR SEQ ID NO:14:                                              (i) SEQUENCE CHARACTERISTICS:                                                  (A) LENGTH: 8 amino acids                                                      (B) TYPE: amino acid                                                           (C) STRANDEDNESS: single                                                       (D) TOPOLOGY: linear,                                                          (ix) FEATURE:                                                                  (A) NAME/KEY: Modified-site                                                    (B) LOCATION: 1                                                                (D) OTHER INFORMATION: /note= "Should be Mpr"                                  (ix) FEATURE:                                                                  (A) NAME/KEY: Modified-site                                                    (B) LOCATION: 2                                                                (D) OTHER INFORMATION: /note= "Should be Har"                                  (xi) SEQUENCE DESCRIPTION: SEQ ID NO:14:                                       XaaXaaGlyAspTrpProAlaCys                                                       15                                                                             (2) INFORMATION FOR SEQ ID NO:15:                                              (i) SEQUENCE CHARACTERISTICS:                                                  (A) LENGTH: 8 amino acids                                                      (B) TYPE: amino acid                                                           (C) STRANDEDNESS: single                                                       (D) TOPOLOGY: linear                                                           (ix) FEATURE:                                                                  (A) NAME/KEY: Modified-site                                                    (B) LOCATION: 1                                                                (D) OTHER INFORMATION: /note= "Should be Mpr"                                  (ix) FEATURE:                                                                  (A) NAME/KEY: Modified-site                                                    (B) LOCATION: 2                                                                (D) OTHER INFORMATION: /note= "Should be Har"                                  (ix) FEATURE:                                                                  (A) NAME/KEY: Modified-site                                                    (B) LOCATION: 7                                                                (C) OTHER INFORMATION: /note= "Should be N-Me-Ala"                             (xi) SEQUENCE DESCRIPTION: SEQ ID NO:15:                                       XaaXaaGlyAspTrpProXaaCys                                                       15                                                                             (2) INFORMATION FOR SEQ ID NO:16:                                              (i) SEQUENCE CHARACTERISTICS:                                                  (A) LENGTH: 8 amino acids                                                      (B) TYPE: amino acid                                                           (C) STRANDEDNESS: single                                                       (D) TOPOLOGY: linear                                                           (ix) FEATURE:                                                                  (A) NAME/KEY: Modified-site                                                    (B) LOCATION: 1                                                                (D) OTHER INFORMATION: /note= "Should be Mpr"                                  (ix) FEATURE:                                                                  (A) NAME/KEY: Modified-site                                                    (B) LOCATION: 2                                                                (D) OTHER INFORMATION: /note= "Should be Har"                                  (xi) SEQUENCE DESCRIPTION: SEQ ID NO:16:                                       XaaXaaGlyAspTrpProGlyCys                                                       15                                                                             (2) INFORMATION FOR SEQ ID NO:17:                                              (i) SEQUENCE CHARACTERISTICS:                                                  (A) LENGTH: 8 amino acids                                                      (B) TYPE: amino acid                                                           (C) STRANDEDNESS: single                                                       (D) TOPOLOGY: linear                                                           (ix) FEATURE:                                                                  (A) NAME/KEY: Modified-site                                                    (B) LOCATION: 1                                                                (D) OTHER INFORMATION: /note= "Should be Mpr"                                  (ix) FEATURE:                                                                  (A) NAME/KEY: Modified-site                                                    (B) LOCATION: 2                                                                (D) OTHER INFORMATION: /note= "Should be Har"                                  (ix) FEATURE:                                                                  (A) NAME/KEY: Modified-site                                                    (B) LOCATION: 7                                                                (c) OTHER INFORMATION: /note= "Should be D-Ala"                                (xi) SEQUENCE DESCRIPTION: SEQ ID NO:17:                                       XaaXaaGlyAspTrpProXaaCys                                                       15                                                                             (2) INFORMATION FOR SEQ ID NO:18:                                              (i) SEQUENCE CHARACTERISTICS:                                                  (A) LENGTH: 8 amino acids                                                      (B) TYPE: amino acid                                                           (C) STRANDEDNESS: single                                                       (D) TOPOLOGY: linear                                                           (ix) FEATURE:                                                                  (A) NAME/KEY: Modified-site                                                    (B) LOCATION: 1                                                                (D) OTHER INFORMATION: /note= "Should be Mpr"                                  (ix) FEATURE:                                                                  (A) NAME/KEY: Modified-site                                                    (B) LOCATION: 2                                                                (D) OTHER INFORMATION: /note= "Should be Har"                                  (xi) SEQUENCE DESCRIPTION: SEQ ID NO:18:                                       XaaXaaGlyAspTrpProProCys                                                       15                                                                             (2) INFORMATION FOR SEQ ID NO:19:                                              (i) SEQUENCE CHARACTERISTICS:                                                  (A) LENGTH: 8 amino acids                                                      (B) TYPE: amino acid                                                           (C) STRANDEDNESS: single                                                       (D) TOPOLOGY: linear                                                           (ix) FEATURE:                                                                  (A) NAME/KEY: Modified-site                                                    (B) LOCATION: 1                                                                (D) OTHER INFORMATION: /note= "Should be Mpr"                                  (ix) FEATURE:                                                                  (A) NAME/KEY: Modified-site                                                    (B) LOCATION: 2                                                                (D) OTHER INFORMATION: /note= "Should be Har"                                  (ix) FEATURE:                                                                  (A) NAME/KEY: Modified-site                                                    (B) LOCATION: 7                                                                (D) OTHER INFORMATION: /note= "Should be Sar"                                  (xi) SEQUENCE DESCRIPTION: SEQ ID NO:19:                                       XaaXaaGlyAspTrpProXaaCys                                                       15                                                                             (2) INFORMATION FOR SEQ ID NO:20:                                              (i) SEQUENCE CHARACTERISTICS:                                                  (A) LENGTH: 8 amino acids                                                      (B) TYPE: amino acid                                                           (C) STRANDEDNESS: single                                                       (D) TOPOLOGY: linear                                                           (ix) FEATURE:                                                                  (A) NAME/KEY: Modified-site                                                    (B) LOCATION: 1                                                                (D) OTHER INFORMATION: /note= "Should be Mpr"                                  (ix) FEATURE:                                                                  (A) NAME/KEY: Modified-site                                                    (B) LOCATION: 2                                                                (D) OTHER INFORMATION: /note= "Should be Har"                                  (ix) FEATURE:                                                                  (A) NAME/KEY: Modified-site                                                    (B) LOCATION: 7                                                                (D) OTHER INFORMATION: /note= "Should be Aib"                                  (xi) SEQUENCE DESCRIPTION: SEQ ID NO:20:                                       XaaXaaGlyAspTrpProXaaCys                                                       15                                                                             (2) INFORMATION FOR SEQ ID NO:21:                                              (i) SEQUENCE CHARACTERISTICS:                                                  (A) LENGTH: 8 amino acids                                                      (B) TYPE: amino acid                                                           (C) STRANDEDNESS: single                                                       (D) TOPOLOGY: linear                                                           (ix) FEATURE:                                                                  (A) NAME/KEY: Modified-site                                                    (B) LOCATION: 1                                                                (D) OTHER INFORMATION: /note= "Should be Mpr"                                  (ix) FEATURE:                                                                  (A) NAME/KEY: Modified-site                                                    (B) LOCATION: 3                                                                (D) OTHER INFORMATION: /note= "Should be Har"                                  (ix) FEATURE:                                                                  (A) NAME/KEY: Modified-site                                                    (B) LOCATION: 8                                                                (D) OTHER INFORMATION: /note= "Should be Pen"                                  (xi) SEQUENCE DESCRIPTION: SEQ ID NO:21:                                       XaaAlaXaaGlyAspTrpProXaa                                                       15                                                                             (2) INFORMATION FOR SEQ ID NO:22:                                              (i) SEQUENCE CHARACTERISTICS:                                                  (A) LENGTH: 8 amino acids                                                      (B) TYPE: amino acid                                                           (C) STRANDEDNESS: single                                                       (D) TOPOLOGY: linear                                                           (ix) FEATURE:                                                                  (A) NAME/KEY: Modified-site                                                    (B) LOCATION: 1                                                                (D) OTHER INFORMATION: /note= "Should be Mpr"                                  (ix) FEATURE:                                                                  (A) NAME/KEY: Modified-site                                                    (B) LOCATION: 8                                                                (D) OTHER INFORMATION: /note= "Should be Pen"                                  (xi) SEQUENCE DESCRIPTION: SEQ ID NO:22:                                       XaaAlaLysGlyAspTrpProXaa                                                       15                                                                             (2) INFORMATION FOR SEQ ID NO:23:                                              (i) SEQUENCE CHARACTERISTICS:                                                  (A) LENGTH: 8 amino acids                                                      (B) TYPE: amino acid                                                           (C) STRANDEDNESS: single                                                       (D) TOPOLOGY: linear                                                           (ix) FEATURE:                                                                  (A) NAME/KEY: Modified-site                                                    (B) LOCATION: 1                                                                (D) OTHER INFORMATION: /note= "Should be Mpr"                                  (ix) FEATURE:                                                                  (A) NAME/KEY: Modified-site                                                    (B) LOCATION: 3                                                                (D) OTHER INFORMATION: /note= "Should be Har"                                  (ix) FEATURE:                                                                  (A) NAME/KEY: Modified-site                                                    (B) LOCATION: 8                                                                (D) OTHER INFORMATION: /note= "Should be Pen"                                  (xi) SEQUENCE DESCRIPTION: SEQ ID NO:23:                                       XaaAspXaaGlyAspTrpProXaa                                                       15                                                                             __________________________________________________________________________ 

We claim:
 1. A peptide selected from the group consisting of:PAI 82 Mpr-A-Har-G-D-W-P-C-NH₂ and (SEQ ID No:3) PAI 92 Mpr-S-Har-G-D-W-P-C-NH₂. (SEQ ID No:13).
 2. The peptide of claim 1, wherein said peptide is a cyclic peptide comprising a bond between a terminal Mpr and a terminal Cys.
 3. The peptide of claim 1, wherein said peptide isPAI 82 Mpr-A-Har-G-D-W-P-C-NH₂. (SEQ ID No:3).
 4. The peptide of claim 1, wherein said peptide isPAI 92 Mpr-S-Har-G-D-W-P-C-NH₂. (SEQ ID No:13). 